[Intel-gfx] [PATCH v4 1/2] drm/i915: DP link training optimization

[Daniel Vetter]

On Wed, Apr 29, 2015 at 11:56:41AM +0530, Sivakumar Thulasimani wrote:
> Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani at intel.com>
> 
> On 4/29/2015 11:47 AM, Mika Kahola wrote:
> >This is a first of series patches that optimize DP link
> >training. The first patch is for eDP only where we reuse
> >the previously trained link training values from cache
> >i.e. voltage swing and pre-emphasis levels.
> >
> >In case we are not able to train the link by reusing
> >the known values, the link training parameters are set
> >to zero and training is restarted.
> >
> >V2:
> >- flag that indicates if DP link is trained and valid
> >   renamed from 'link_trained' to 'train_set_valid'
> >- removed routine 'intel_dp_reuse_link_train'
> >
> >V3:
> >- rebased against the latest drm-intel-nightly
> >
> >V4:
> >- removed HPD long pulse handling for eDP case to clear the
> >   flag that indicates to reuse the current link training
> >   parameters. (based on Sivakumar's comment)
> >
> >Signed-off-by: Mika Kahola <mika.kahola at intel.com>

Both merged, with an s/DP/eDP/ on this one to make the different scope of
the 2 patches clear. Two patches with the same summary is confusing ;-)

Thanks, Daniel
> >---
> >  drivers/gpu/drm/i915/intel_dp.c  | 27 ++++++++++++++++++++++++---
> >  drivers/gpu/drm/i915/intel_drv.h |  1 +
> >  2 files changed, 25 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> >index 937ba31..e0b35cb 100644
> >--- a/drivers/gpu/drm/i915/intel_dp.c
> >+++ b/drivers/gpu/drm/i915/intel_dp.c
> >@@ -3547,7 +3547,8 @@ static bool
> >  intel_dp_reset_link_train(struct intel_dp *intel_dp, uint32_t *DP,
> >  			uint8_t dp_train_pat)
> >  {
> >-	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> >+	if (!intel_dp->train_set_valid)
> >+		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> >  	intel_dp_set_signal_levels(intel_dp, DP);
> >  	return intel_dp_set_link_train(intel_dp, DP, dp_train_pat);
> >  }
> >@@ -3660,6 +3661,23 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
> >  			break;
> >  		}
> >+		/*
> >+		 * if we used previously trained voltage and pre-emphasis values
> >+		 * and we don't get clock recovery, reset link training values
> >+		 */
> >+		if (intel_dp->train_set_valid) {
> >+			DRM_DEBUG_KMS("clock recovery not ok, reset");
> >+			/* clear the flag as we are not reusing train set */
> >+			intel_dp->train_set_valid = false;
> >+			if (!intel_dp_reset_link_train(intel_dp, &DP,
> >+						       DP_TRAINING_PATTERN_1 |
> >+						       DP_LINK_SCRAMBLING_DISABLE)) {
> >+				DRM_ERROR("failed to enable link training\n");
> >+				return;
> >+			}
> >+			continue;
> >+		}
> >+
> >  		/* Check to see if we've tried the max voltage */
> >  		for (i = 0; i < intel_dp->lane_count; i++)
> >  			if ((intel_dp->train_set[i] & DP_TRAIN_MAX_SWING_REACHED) == 0)
> >@@ -3737,6 +3755,7 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
> >  		/* Make sure clock is still ok */
> >  		if (!drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)) {
> >+			intel_dp->train_set_valid = false;
> >  			intel_dp_start_link_train(intel_dp);
> >  			intel_dp_set_link_train(intel_dp, &DP,
> >  						training_pattern |
> >@@ -3752,6 +3771,7 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
> >  		/* Try 5 times, then try clock recovery if that fails */
> >  		if (tries > 5) {
> >+			intel_dp->train_set_valid = false;
> >  			intel_dp_start_link_train(intel_dp);
> >  			intel_dp_set_link_train(intel_dp, &DP,
> >  						training_pattern |
> >@@ -3773,9 +3793,10 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
> >  	intel_dp->DP = DP;
> >-	if (channel_eq)
> >+	if (channel_eq) {
> >+		intel_dp->train_set_valid = is_edp(intel_dp);
> >  		DRM_DEBUG_KMS("Channel EQ done. DP Training successful\n");
> >-
> >+	}
> >  }
> >  void intel_dp_stop_link_train(struct intel_dp *intel_dp)
> >diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> >index 43fe003..94197bd 100644
> >--- a/drivers/gpu/drm/i915/intel_drv.h
> >+++ b/drivers/gpu/drm/i915/intel_drv.h
> >@@ -736,6 +736,7 @@ struct intel_dp {
> >  				     bool has_aux_irq,
> >  				     int send_bytes,
> >  				     uint32_t aux_clock_divider);
> >+	bool train_set_valid;
> >  	/* Displayport compliance testing */
> >  	unsigned long compliance_test_type;
> 
> -- 
> regards,
> Sivakumar
> 
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> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch